The Arabidopsis Heterochronic Gene ZIPPY Is an ARGONAUTE Family Member

Hunter, Christine; Sun, Hui; Poethig, R. Scott

doi:10.1016/j.cub.2003.09.004

Cited by 214 publications

(165 citation statements)

References 33 publications

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“…Following unwinding of dicer-generated 20-25-bp duplexes, singlestranded siRNAs or miRNAs are loaded into RISCs that participate in subsequent steps, such as mRNA inactivation or heterochromatin modification. A defining component of RISC RNP complexes is an Argonaute (AGO) protein, a family of proteins that is conserved from fission yeast to humans and gets its name from its founding member in Arabidopsis (Carmell et al 2002;Hunter et al 2003;Sasaki et al 2003;Sontheimer and Carthew 2004).In addition to Dicer and Argonaute proteins, Neurospora, plants, Schizosaccharomyces pombe, and Caenorhabditis elegans make use of RNA-dependent RNA polymerases (RdRPs) for RNA silencing (Wassenegger and Krczal 2006). Neurospora and tomato RdRPs have been shown to synthesize dsRNA, in a primer-independent fashion, from a single-stranded RNA template in vitro (Schiebel et al 1993;Makeyev and Bamford 2002).…”

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confidence: 99%

Cell Biology of the Arabidopsis Nuclear siRNA Pathway for RNA-directed Chromatin Modification

Pikaard¹

2006

Cold Spring Harbor Symposia on Quantitative Biology

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473In diverse eukaryotes, small RNAs have important roles in viral defense, centromere maintenance, or transcriptional silencing of transposons and repeated DNA elements. These RNA-mediated gene silencing phenomena can occur posttranscriptionally, due to inactivation of homologous target RNAs, or transcriptionally, by specifying repressive heterochromatin formation at DNA sequences that match the small RNAs (Baulcombe 2004;Grewal and Rice 2004;Lippman and Martienssen 2004;Almeida and Allshire 2005;Brodersen and Voinnet 2006). The various forms of RNA silencing have in common the involvement of 21-25-nucleotide RNAs, known as siRNAs or microRNAs (miRNAs), that are generated from double-stranded RNA (dsRNA) precursors by RNase-III-like endonucleases known as Dicers (Bernstein et al. 2001;Hannon 2002). Following unwinding of dicer-generated 20-25-bp duplexes, singlestranded siRNAs or miRNAs are loaded into RISCs that participate in subsequent steps, such as mRNA inactivation or heterochromatin modification. A defining component of RISC RNP complexes is an Argonaute (AGO) protein, a family of proteins that is conserved from fission yeast to humans and gets its name from its founding member in Arabidopsis (Carmell et al. 2002;Hunter et al. 2003;Sasaki et al. 2003;Sontheimer and Carthew 2004).In addition to Dicer and Argonaute proteins, Neurospora, plants, Schizosaccharomyces pombe, and Caenorhabditis elegans make use of RNA-dependent RNA polymerases (RdRPs) for RNA silencing (Wassenegger and Krczal 2006). Neurospora and tomato RdRPs have been shown to synthesize dsRNA, in a primer-independent fashion, from a single-stranded RNA template in vitro (Schiebel et al. 1993;Makeyev and Bamford 2002). The Neurospora RdRP also has been shown to be capable of using short RNA primers for dsRNA synthesis (Makeyev and Bamford 2002), suggesting that siRNAs might prime dsRNA synthesis by RdRP, leading to dicing and amplification of siRNAs as long as the target RNA continues to be produced (Baulcombe 2004).Plants possess a diversified tool kit for conducting RNA silencing, including four Dicers (DCL1-DCL4), ten Argonautes (AGO1-AGO10), and six RdRPs The ten Arabidopsis Argonaute proteins also have specialized functions. For instance, AGO1 is involved in miRNA-and siRNA-dependent mRNA degradation pathways , whereas AGO4 functions in the pathway for siRNA-directed DNA methylation and chromatin modification Vaucheret et al. 2004). Likewise, the six RdRPs appear to have different roles in the cell, with RDR6 required for viral, transgene, and trans-acting siRNA production and RDR2 specializing in the siRNA-directed DNA methylation and chromatin modification pathway (Baulcombe 2004;Peragine et al. 2004;Vazquez et al. 2004;Xie et al. 2004;Allen et al. 2005). This paper focuses on the siRNA-directed DNA methylation and chromatin modification pathway that, in addition to DCL3, RDR2, and AGO4 introduced above, In Arabidopsis thaliana, the pathway for transcriptional silencing via RNA-directed DNA methylation and chromatin modification involv...

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confidence: 99%

Cell Biology of the Arabidopsis Nuclear siRNA Pathway for RNA-directed Chromatin Modification

Pikaard¹

2006

Cold Spring Harbor Symposia on Quantitative Biology

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“…RDR6 has also been implicated in natural virus resistance (Qu et al, 2005). ZIP encodes ARGONAUTE7 (AGO7) whose primary function is in the regulation of developmental timing (Hunter et al, 2003). DCL4 produces 21 nt RDR6-dependent ta-siRNAs and has been reported to participate in siRNA production following viral infections In wt Col-0 Arabidopsis, the first two rosette leaves appeared round and relatively flat (Fig.…”

Section: Resultsmentioning

confidence: 99%

Hibiscus chlorotic ringspot virus coat protein inhibits trans-acting small interfering RNA biogenesis in Arabidopsis

Meng

Chen

Ding

et al. 2008

Journal of General Virology

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Many plant and animal viruses have evolved suppressor proteins to block host RNA silencing at various stages of the RNA silencing pathways. Hibiscus chlorotic ringspot virus (HCRSV) coat protein (CP) is capable of suppressing the transiently expressed sense-RNA-induced posttranscriptional gene silencing (PTGS) in Nicotiana benthamiana. Here, constitutively expressed HCRSV CP from transgenic Arabidopsis was found to be able to rescue expression of the silenced GUS transgene. The HCRSV CP-transgenic Arabidopsis (line CP6) displayed several developmental abnormalities: elongated, downwardly curled leaves and a lack of coordination between stamen and carpel, resulting in reduced seed set. These abnormalities are similar to those observed in mutations of the genes of Arabidopsis RNA-dependent polymerase 6 (rdr6), suppressor of gene silencing 3 (sgs3), ZIPPY (zip) and dicer-like 4 (dcl4). The accumulation of microRNA (miRNA) miR173 remained stable; however, the downstream trans-acting small interfering RNA (ta-siRNA) siR255 was greatly reduced. Real-time PCR analysis showed that expression of the ta-siRNA-targeted At4g29770, At5g18040, PPR and ARF3 genes increased significantly, especially in the inflorescences. Genetic crossing of CP6 with an amplicon-silenced line (containing a potato virus X-green fluorescent protein transgene under the control of the 35S cauliflower mosaic virus promoter) suggested that HCRSV CP probably interfered with gene silencing at a step after RDR6. The reduced accumulation of ta-siRNA might result from the interference of HCRSV CP with Dicer-like protein(s), responsible for the generation of dsRNA in ta-siRNA biogenesis. INTRODUCTIONSmall-RNA-mediated silencing pathways play important roles in a variety of processes, including defence against viruses. Viruses in turn evolve mechanisms to interfere with the host silencing responses for successful infection, which usually results in differential developmental defects. The molecular basis of gene-silencing-related abnormal development is mediated by a group of small RNAs, including microRNAs (miRNAs) and small interfering RNAs (siRNAs) (Bartel, 2004;Baulcombe, 2004; JonesRhoades et al., 2006). The miRNAs are a class of small RNAs similar to siRNAs that are key components of the complex networks of gene regulatory pathways. As most plant miRNAs contain near-perfect complementarities with target sequences, they are thought to function like siRNAs in guiding target RNA for cleavage (Rhoades et al., 2002). In Arabidopsis thaliana, there are four Dicer-like proteins (DCLs) that are responsible for the production of miRNAs and siRNAs of different sizes. All four DCLs act in combination to help mediate plant responses to diverse viral infections (Blevins et al., 2006;Deleris et al., 2006).The plant miRNAs target a series of genes/gene families that are important for normal plant development (Kidner & Martienssen, 2005). Interference in miRNA biogenesis or miRNA-target interactions lead to developmental abnormalities (Bartel & Bartel, 2003;Dugas & Ba...

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“…It is through posttranscriptional gene silencing that AGO1 mediates vegetative leaf and pollen development [73][74][75]. Other roles observed for AGO proteins include AGO4-directed DNA methylation and silencing of transposons [76] and the ZIP/AGO7-mediated regulation of developmental timing and proposed ta-siRNA pathway constituent [59,77,78]. One AGO protein has been implicated in both rice development and the RNA production pathway.…”

Section: Rice Mutants In Small Rna Biogenesis Pathwaysmentioning

confidence: 99%

The Cornucopia of Small RNAs in Plant Genomes

Simon

Zhai

Zeng

2008

Rice

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Regulatory small RNAs (approximately 20 to 24 nt in length) are produced through pathways that involve several key evolutionarily conserved protein families; the variants of these proteins found in plants are encoded by multigene families and are known as Dicer-like, Argonaute, and RNA-dependent RNA polymerase proteins. Small RNAs include the well-known classes of microRNAs (miRNAs, 21 nt) and the small-interfering RNAs (siRNAs,~24 nt). Both of these types of molecules are found across a broad set of eukaryotic species, although the siRNAs are a much larger and more diverse class in plants due to the abundance of heterochromatic siRNAs. Well-studied species such as Arabidopsis have provided a foundation for understanding in rice and other species how small RNAs function as key regulators of gene expression. In this paper, we review the current understanding of plant small RNA pathways, including the biogenesis and function of miRNAs, siRNAs, trans-acting siRNAs, and heterochromatic siRNAs. We also examine the evolutionary relationship among plant species of both their miRNAs and the key enzymatic components of the small RNA pathways. Many of the most recent advances in describing small RNAs have resulted from advances in sequencing technologies used for identifying and measuring small RNAs, and these technologies are discussed. Combined with the plethora of genetic tools available to researchers, we expect that the continued elucidation of the identity and functions of plant small RNAs will be both exciting and rewarding.

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The Arabidopsis Heterochronic Gene ZIPPY Is an ARGONAUTE Family Member

Cited by 214 publications

References 33 publications

Cell Biology of the Arabidopsis Nuclear siRNA Pathway for RNA-directed Chromatin Modification

Cell Biology of the Arabidopsis Nuclear siRNA Pathway for RNA-directed Chromatin Modification

Hibiscus chlorotic ringspot virus coat protein inhibits trans-acting small interfering RNA biogenesis in Arabidopsis

The Cornucopia of Small RNAs in Plant Genomes

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